A neural probe with up to 966 electrodes and up to 384 configurable channels in 0.13 μm SOI CMOS

In vivo recording of neural action-potential and local-field-potential signals requires the use of high-resolution penetrating probes. Several international initiatives to better understand the brain are driving technology efforts towards maximizing the number of recording sites while minimizing the neural probe dimensions. We designed and fabricated (0.13-μm SOI Al CMOS) a 384-channel configurable neural probe for large-scale in vivo recording of neural signals. Up to 966 selectable active electrodes were integrated along an implantable shank (70 μm wide, 10 mm long, 20 μm thick), achieving a crosstalk of −64.4 dB. The probe base (5 × 9 mm2) implements dual-band recording and a 1

Time Multiplexed Active Neural Probe with 678 Parallel Recording Sites

We present a high density CMOS neural probe with active electrodes (pixels), consisting of dedicated in-situ circuits for signal source amplification. The complete probe contains 1356 neuron size (20x20 μm2) pixels densely packed on a 50 μm thick, 100 μm wide and 8 mm long shank. It allows simultaneous highperformance recording from 678 electrodes and a possibility to simultaneously observe all of the 1356 electrodes with increased noise. This considerably surpasses the state of the art active neural probes in electrode count and flexibility. The measured action potential band noise is 12.4 μVrms, with just 3 μW power dissipation per electrode amplifier and 45 μW per channel (including data transmission)

Time Multiplexed Active Neural Probe with 1356 Parallel Recording Sites

We present a high electrode density and high channel count CMOS (complementary metal-oxide-semiconductor) active neural probe containing 1344 neuron sized recording pixels (20 µm × 20 µm) and 12 reference pixels (20 µm × 80 µm), densely packed on a 50 µm thick, 100 µm wide, and 8 mm long shank. The active electrodes or pixels consist of dedicated in-situ circuits for signal source amplification, which are directly located under each electrode. The probe supports the simultaneous recording of all 1356 electrodes with sufficient signal to noise ratio for typical neuroscience applications. For enhanced performance, further noise reduction can be achieved while using half of the electrodes (678). Both of these numbers considerably surpass the state-of-the art active neural probes in both electrode count and number of recording channels. The measured input referred noise in the action potential band is 12.4 µVrms, while using 678 electrodes, with just 3 µW power dissipation per pixel and 45 µW per read-out channel (including data transmission)

Mixed-signal template-based reduction scheme for stimulus artifact removal in electrical stimulation

Simultaneous electrical stimulation and recording are used to gain insights into the function of neuronal circuitry. However, artifacts produced by the electrical stimulation pulses prevent the recording of neural responses during, and a short period after, the stimulation duration. In this work, we describe a mixed-signal recording topology with template subtraction for removing the artifact during the stimulation pulse. Emulated artifacts generated from a lumped electrical circuit model and experimental artifacts in cardiac cell cultures are used to evaluate the topology. The simulations show that delays between the emulated artifact and its estimated compensation template represent the largest error source of the analog template subtraction. The quantization error appears like random noise and determines the threshold level for the action potential detection. Simulations show that removal of the artifacts is possible, allowing the detection of action potentials during the stimulation pulsing period, even for high-amplitude saturating artifacts. Measurement results with artifacts elicited in cardiac cell cultures show feasible applications of this topology. The proposed topology therefore promisingly opens up a previously unavailable detection window for improving the analysis of the neuronal activity.status: publishe

Coulometric Detection of Irreversible Electrochemical Reactions Occurring at Pt Microelectrodes Used for Neural Stimulation

The electrochemistry of 50 mu m diameter Pt electrodes used for neural stimulation was studied in vitro by reciprocal derivative chronopotentiometry. This differential method provides well-defined electrochemical signatures of the various polarization phenomena that occur at Pt microelectrodes and are generally obscured in voltage transients. In combination with a novel in situ coulometric approach, irreversible H-2 and O-2 evolution, Pt dissolution and reduction of dissolved O-2 were detected. Measurements were performed with biphasic, charge-balanced, cathodic-first and anodic-first current pulses at charge densities ranging from 0.07 to 1.41 mC/cm(2) (real surface area) in phosphate buffered saline (PBS) with and without bovine serum albumin (BSA). The extent to which O-2 reduction occurs under the different stimulation conditions was compared in O-2-saturated and deoxygenated PBS. Adsorption of BSA inhibited Pt dissolution as well as Pt oxidation and oxide reduction by blocking reactive sites on the electrode surface. This inhibitory effect promoted the onset of irreversible H-2 and O-2 evolution, which occurred at lower charge densities than those in PBS. Reduction of dissolved O-2 on Pt electrodes accounted for 19-34% of the total injected charge in O-2-saturated PBS, while a contribution of 0.4-12% was estimated for in vivo stimulation. These result may prove important for the interpretation of histological damage induced by neural stimulation and therefore help define safer operational limits.status: publishe

Prozesstechnologien zur Herstellung kontinuierlich faserverstaerkter thermoplastischer Halbzeuge

Continuous fibre reinforced thermoplastics are a high competitive material class for diversified applications because of their inherent properties like light-weight construction potential, integral design, corrosion resistance and high energy absorption level. Using these materials, one approach towards a large volume scaled part production rate is covered by an automated process line, consisting of a pressing process for semi-finished sheet material production, a thermoforming step and some additional joining technologies. To allow short cycle times in the thermoforming step, the utilised semi-finished sheet materials, which are often referred to as 'oganic sheets', have to be fully impregnated and consolidated. Nowadays even this combination of outstanding physical and chemical material properties combined with the economic processing technology are no guarantee for the break-through of continuous fibre reinforced thermoplastics, mainly because of the high material costs for the semi-finished sheet materials. These costs can be attributed to a non adapted material selection or choice of process parameters, as well as by unfavourable pressing process type itself. Therefore the aim of the present investigations was to generate some alternatives regarding the choice of raw materials, the set-up or the selection of the pressing process line and to provide some theoretical tools for the determination of process parameters and dimensions. Concerning raw material aspects, the use of the blending technology is one promising approach towards cost reduction for the matrix component. Novel characteristics related to the fibre structure are CF-yarns with high filament numbers (e.g. 6 K or 12 K instead of 3 K) or multiaxial fibre orientations. These two approaches were both conducted for sheet materials with carbon fibre reinforcement and high temperature thermoplastics. Two new developed ternary blend matrices consisting of PEEK and PEI as the main ingredients were tested in comparison with neat PEEK. PES and PSU were used as the third blend component, which provides a cost reduction potential approximately 30% compared to the basis PEEK polymer. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Using reciprocal derivative chronopotentiometry as a technique to determine safe charge injection limits of electrodes used for neural stimulation

We used reciprocal derivative chronopotentiometry (RDC) with platinum electrodes of 50 μm diameter in 0.15 M phosphate buffered saline solution to identify the various elec- trochemical processes occurring at the electrode during biphasic current pulsing. RDC allowed to determine the limits of water hydrolysis based on the specific (dt/dE)−E data representation employed in this technique resulting in curves similar to the voltammetric i−E response. Current stimulation was performed by either varying the pulse amplitude or pulse width. We found that the limits for H2 and O2 evolution for constant-amplitude pulses lied at 0.51 mC/cm2 and 0.67 mC/cm2, respectively, while for constant-width pulses they occurred at slightly lower values of 0.49 mC/cm2 and 0.61 mC/cm2, respectively. We could also extract values for the anodic and cathodic overvoltages associated with gas evolution. The cathodic overvoltage for H2 evolution was 1.43 V for both constant-amplitude and constant-width pulses, while the anodic overpotentials for O2 evolution were 2.45 V in the first and 2.24 V in the latter case. These values are clearly larger than the gas evolution limits generally found with steady- state voltammetry.status: publishe